Method for manufacturing solar cell, photovoltaic cell and photovoltaic module

Abstract

This invention relates to the field of photovoltaic cell technology, and more particularly to a solar cell, a method for fabricating a photovoltaic cell, and a photovoltaic module. The solar cell includes: a silicon substrate; a trench formed on the silicon substrate; a heavily doped layer formed on the inner surface of the trench; an interface passivation layer formed on the heavily doped layer; and a metal electrode structure formed within the trench and in contact with the interface passivation layer; wherein the doping concentration of the heavily doped layer is greater than the doping concentration of the surrounding silicon substrate material. This application utilizes a three-step synergistic process of "grooving—selective heavy doping—ultra-thin interface passivation" to precisely construct an electrode contact region with both ultra-low contact resistance and excellent interface passivation quality within a micrometer-level trench, providing a core guarantee for the cell to obtain a high open-circuit voltage, and achieving the technical effects of high conductivity, low recombination, and low cost in solar cells.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cell technology, and in particular to a solar cell, a method for preparing a photovoltaic cell, and a photovoltaic module. Background Technology

[0002] Currently, the mainstream method for forming the metal electrode structure of solar cells is usually based on screen-printed silver paste technology. Although this technology is mature, it has inherent limitations: First, in order to form a good ohmic contact and withstand high-temperature sintering, a large area of ​​heavy doping is required under the electrode, which introduces severe carrier recombination and limits the improvement of the cell's open-circuit voltage; second, the silver paste has a high resistivity, and in order to reduce the grid line resistance, the printing amount needs to be increased, resulting in high costs and potential risks related to adhesion and pull; third, the printing precision is limited, making it difficult to achieve finer electrode patterns with higher aspect ratios to reduce contact area and light shading.

[0003] Therefore, developing a novel metal electrode structure and preparation method that can synergistically optimize contact electrical performance, interface passivation quality, electrode conductivity and mechanical reliability at the microscale is of urgent need and great significance for promoting the industrialization of back contact batteries. Summary of the Invention

[0004] The first objective of this invention is to provide a solar cell to solve at least one of the aforementioned technical problems in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A solar cell, comprising: Silicon substrate; Trenches are formed on the silicon substrate; A heavily doped layer is formed on the inner surface of the trench; An interface passivation layer is formed on the heavily doped layer; a metal electrode structure is formed in the trench and is in contact with the interface passivation layer; The doping concentration of the heavily doped layer is greater than that of the surrounding silicon substrate material.

[0006] This application employs a three-step synergistic process of "grooving—selective heavy doping—ultra-thin interface passivation" to precisely construct electrode contact regions with both ultra-low contact resistance and excellent interface passivation quality within micron-level trenches. This composite interface structure design ensures excellent ohmic contact between the metal and semiconductor while minimizing recombination losses in the metal-semiconductor contact area. Simultaneously, the doping concentration in the non-metallic contact area of ​​the semiconductor is significantly lower than that in the metallic contact area, providing a core guarantee for achieving high open-circuit voltage in the cell. This achieves the technical effects of high conductivity, low recombination, and low cost in solar cells. Furthermore, compared to conventional methods that form metal electrode structures through printing processes, the metal electrode structure in this application is directly embedded within the trench, offering advantages such as a larger contact area, less electrode detachment, smaller cell light-shielding area, and better silicon substrate surface flatness.

[0007] In this embodiment, at least one of the light-facing and back-light-facing surfaces of the silicon substrate is provided with multiple metal electrode structures, and the metal electrode structures on the same surface are arranged according to a preset electrode pattern. All the metal electrode structures are divided into first metal electrode structures and second metal electrode structures with different polarities. In some embodiments, the first metal electrode structures and the second metal electrode structures are alternately arranged along the first direction on the back-light-facing surface; in this embodiment, the solar cell is a back-contact solar cell. In other embodiments, the first metal electrode structures and the second metal electrode structures are alternately arranged along the first direction on the light-facing surface and the back-light-facing surface, respectively; in this embodiment, the solar cell is a bifacial solar cell. In still other embodiments, the first metal electrode structures are sequentially arranged along the first direction on the light-facing surface, and the second metal electrode structures are sequentially arranged along the first direction on the back-light-facing surface; in this embodiment, the solar cell is also a bifacial solar cell. Furthermore, this solar cell can be a multi-busbar cell or an OBB cell.

[0008] In some embodiments, the doping concentration of the heavily doped layer is 1×10¹ 9 atoms / cm³ ~1×10²¹atoms / cm³; And / or, the doping concentration of the silicon substrate material surrounding the heavily doped layer is 1 × 10¹ 5 atoms / cm³ ~1×10¹ 7 atoms / cm³; And / or, the ratio of the doping concentration of the heavily doped layer to the doping concentration of the surrounding silicon substrate material is 100:1 to 10000:1.

[0009] The doping concentration of the heavily doped layer and the surrounding silicon substrate material can be selected from the above-mentioned preferred range.

[0010] In some embodiments, the material of the interface passivation layer is at least one of silicon oxide, aluminum oxide, silicon oxynitride, silicon nitride, silicon carbide, and amorphous silicon; And / or, the thickness of the interface passivation layer is 1~20 nm.

[0011] The material and thickness of the interface passivation layer can be varied within the aforementioned preferred range. The main function of the interface passivation layer is to reduce interfacial recombination. The thickness of the interface passivation layer should not be too thin, as this will lead to poor surface recombination reduction. Simultaneously, the thickness of the interface passivation layer should not be too thick, as this will affect carrier transport efficiency. Setting the thickness of the interface passivation layer within the range of 1~20 nm achieves a good effect in reducing interfacial recombination without affecting carrier transport efficiency. Preferably, the thickness of the interface passivation layer is 1~3 nm, a thickness range that ensures that the interface passivation layer can achieve tunneling conduction.

[0012] In some embodiments, the metal electrode structure protrudes a certain height relative to the surface of the trench. This protruding metal electrode structure has the following advantages: it facilitates the interconnection between the electrode and the solder strip, avoiding the problem of poor contact between the electrode and the solder strip; it increases the cross-sectional area of ​​the electrode, thereby reducing the electrode resistance; and the protruding electrode can protect the heavily doped layer and the interface passivation layer inside the trench from being damaged or destroyed by subsequent processes.

[0013] In other embodiments, the surface of the metal electrode structure near the trench opening is flush with the surface of the trench. This structure, where the surface of the metal electrode is flush with the surface of the trench, has the following advantages: high flatness of the silicon substrate surface and small light-shielding area, reducing the risk of the electrode being bumped or damaged by the external environment. However, this structure is not conducive to the interconnection of the electrode and the solder ribbon, and is more suitable for applications involving metal wiring connections.

[0014] In some embodiments, the cross-sectional shape of the trench is at least one of trapezoidal, U-shaped, arc-shaped, rectangular, and triangular.

[0015] The cross-sectional shape of the trench can be selected from the above range. Preferably, the cross-sectional shape of the trench is trapezoidal. The trapezoidal trench design enables mechanical locking of the electrodes, improving the battery fill factor while giving the electrodes excellent mechanical adhesion and long-term reliability.

[0016] In some embodiments, the opening area of ​​the trench increases from the bottom to the opening. Using this technical solution, after the metal electrode structure is filled into the trench, it forms a reliable, self-locking interconnected structure with the trench, thereby increasing the bonding strength between the metal electrode structure and the silicon substrate, preventing the metal electrode structure from detaching, and improving the performance and reliability of the battery. In other embodiments, the opening area of ​​the trench may decrease from the bottom to the opening.

[0017] In some embodiments, the trench includes a merging trench and a collecting trench. The merging trench extends along a second direction. At least one side of the merging trench in the width direction is arranged with a plurality of collecting trenches at intervals along the second direction. Each collecting trench extends along a first direction. The merging trench and the collecting trench are intersecting and connected. The first direction intersects the second direction. The width of the merging trench is 80~300μm and its depth is 15~20μm. The width of each collecting trench is 20~40μm and its depth is 10~15μm.

[0018] In the trenches provided in the above embodiments, the busbar trench is filled with bus electrodes (commonly known as main grids) for merging current and connecting external conductors, while the collector trench is filled with collector electrodes (commonly known as fine grids) for collecting current. The bus electrodes are generally wider and thicker than the collector electrodes; correspondingly, the busbar trenches generally need to be wider and deeper than the collector trenches. In some other embodiments, the trenches can be elongated strips. In still other embodiments, the trenches may only include collector trenches and not busbar trenches; this trench structure is applied in gridless solar cells.

[0019] In some embodiments, the metal electrode structure includes: A seed layer covers the inner surface of the trench; An electrode body layer is disposed on the seed layer and completely fills the trench; A protective layer covers the surface of the electrode body layer exposed outside the trench.

[0020] The process involves: a seed layer covering at least the bottom of the trench, a sintered conductive metal layer serving as the substrate for subsequent electroplating; an electrode body layer deposited on top of the seed layer and completely filling the trench via electroplating, used for carrier collection and current conduction; and a protective layer covering the surface of the electrode body layer to prevent electrode oxidation and corrosion, improving long-term reliability. Furthermore, the protective layer interconnects with the silicon substrate to form a mechanical locking structure of "in-trench filling + trench opening sealing," ensuring good ohmic contact while locking the electrode body layer within the trench, thus preventing the metal electrode structure layer from peeling off.

[0021] In some embodiments, the seed layer is made of at least one of silver, silver-aluminum alloy, and nickel; And / or, the thickness of the seed layer is 0.5~3μm; And / or, the electrode body layer is an electroplated copper layer; And / or, the protective layer is made of tin or a tin alloy; And / or, the thickness of the protective layer is 0.5~3μm.

[0022] The materials and thicknesses of each layer of the metal electrode structure can be selected from the above-mentioned preferred range.

[0023] A second objective of this invention is to provide a method for preparing a photovoltaic cell, the method comprising the following steps: Provide silicon substrate; Laser grooving: Laser scanning is performed at a predetermined position on the silicon substrate according to a predetermined pattern to form a groove; Forming a heavily doped layer: A heavily doped layer is formed on the inner surface region of the trench by laser doping, wherein the doping concentration of the heavily doped layer is greater than the doping concentration of the surrounding silicon substrate material; Forming an interface passivation layer: An interface passivation layer is formed on the inner surface of the trench by a deposition process; A metal electrode structure is formed that fills the trench.

[0024] Compared to existing technologies that form metal electrode structures through printing or electroplating processes, this method offers several advantages: First, an interface passivation layer is added between the metal electrode structure and the inner surface of the trench. This passivation layer reduces the recombination rate at the metal-semiconductor interface and enhances the adhesion of the metal electrode structure, preventing it from detaching. Second, the metal electrode structure formed by this method is directly embedded in the trench, resulting in a larger contact area, less electrode detachment, a smaller light-shielding area, and better surface flatness of the silicon substrate. Third, the use of a highly efficient laser doping process to replace part of the high-temperature diffusion doping process significantly improves battery conversion efficiency while substantially reducing electrode manufacturing costs, demonstrating outstanding prospects for industrial application and market competitiveness.

[0025] This method employs a three-step synergistic process of "grooving—selective heavy doping—ultra-thin interface passivation" to precisely construct an electrode contact region with both ultra-low contact resistance and excellent interface passivation quality within a micrometer-scale trench, thereby achieving the technical effects of high conductivity, low recombination, and low cost in solar cells.

[0026] In some embodiments, the step of forming a metal electrode structure filling the trench includes: Printing and sintering seed layer: The conductive paste is filled into the trench, pre-dried, and then sintered at low temperature to form a seed layer covering the inner surface of the trench; Electrode body layer deposition: Using the seed layer as the cathode, copper material is deposited on the seed layer by electroplating until the copper material fills the trench and forms an electrode body layer protruding from the surface of the trench; A protective layer is deposited by a deposition process to form a protective layer on the surface of the electrode body layer exposed outside the trench.

[0027] This method employs a composite process of "printed nano-seed layer + electroplated copper + deposited protective layer" to fabricate metal electrode structures, achieving high-precision forming and ultra-low volume resistivity. The electrode body layer perfectly fills the grooves and reliably interconnects, while the protective layer ensures the long-term corrosion resistance of the electrode body layer. Furthermore, the protective layer interconnects with the silicon substrate to form a mechanical locking structure of "groove filling + groove sealing," ensuring good ohmic contact while locking the electrode body layer within the grooves, thus preventing the metal electrode structure layers from peeling off.

[0028] In some embodiments, in the steps of printing and sintering the seed layer: the pre-drying temperature is 100~200℃, and the time is 60~300s; the peak temperature of low-temperature sintering is 250~450℃, and the holding time is 30~300s; the thickness of the seed layer after drying is 1~5μm. And / or, in the step of depositing the electrode body layer: the electroplating process is pulse electroplating or DC electroplating, the plating solution contains copper ions, acid, conductive salt, chloride ions and organic additives, the electroplating process is carried out at a temperature of 20~60°C, and the cathode current density is 1~10A / dm². And / or, in the step of depositing the protective layer: the type of deposition process is one of electroplating deposition, electroless plating deposition, or hot-dip plating deposition, and the thickness of the protective layer is 0.5~3μm.

[0029] The process parameters for the metal electrode structure can be selected within the aforementioned optimal range.

[0030] In some embodiments, in the laser grooving step: a UV picosecond laser or an infrared picosecond laser is used for laser scanning, and the laser scanning parameters are a single pulse energy of 10~50μJ, a repetition frequency of 50~500kHz, and a scanning speed of 0.5~5m / s. During the laser scanning process, gas side blowing is used to remove the molten material.

[0031] The process parameters for the trench can be selected within the aforementioned optimal range.

[0032] In some embodiments, after the laser grooving step, the method for preparing the photovoltaic cell further includes: cleaning the trench: soaking or spraying the trench with a chemical cleaning solution at room temperature, rinsing with ultrapure water and drying with nitrogen after the treatment is completed.

[0033] In the trench cleaning step, the trench is immersed or sprayed with a 1%~5% (w / w) dilute hydrofluoric acid solution and / or buffered oxide etching solution at room temperature for 30~180s to remove etching byproducts and damage to the trench wall, laying the foundation for achieving ultra-low contact resistance and ultra-low interface composite in the trench.

[0034] In some embodiments, the step of forming a heavily doped layer includes: coating a boron- or phosphorus-containing liquid composition into a trench; after pre-drying, precisely scanning the trench with a laser beam to locally melt the silicon substrate material in the trench and incorporate boron or phosphorus atoms to form a P-type or N-type heavily doped region.

[0035] In the step of forming the heavily doped layer: the pre-drying temperature after coating with the boron- or phosphorus-containing liquid composition is 100~200°C, and the time is 60~300s; the laser beam is a continuous wave laser or a long pulse laser with a pulse width greater than 1μs, and the scanning speed is 1~10m / s; for the P-type heavily doped layer, the laser scanning power is 10~50W; for the N-type heavily doped layer, the laser scanning power is 8~40W.

[0036] In solar cell fabrication, the doping order of P-type and N-type doped regions is not critical; the P-type doped regions can be formed first, followed by the N-type doped regions, or vice versa. After doping is complete, the solar cell is cleaned to remove any remaining dopant.

[0037] In some embodiments, after the step of forming the heavily doped layer, the method for preparing the photovoltaic cell further includes an annealing process.

[0038] In the annealing process, a rapid thermal annealing process is employed under a nitrogen or argon atmosphere. The annealing temperature is 800-1000℃, and the annealing time is 10-60 seconds. Annealing the structure not only repairs defects and surface damage caused by the etching process but also effectively activates impurities, providing a fundamental guarantee for achieving ultra-low contact resistance and ultra-low interface composite properties in subsequent processes.

[0039] In some embodiments, after the step of forming a metal electrode structure filling the trench, the method for fabricating the photovoltaic cell further includes: light injection treatment and surface cleaning.

[0040] In the light injection process: the solar cell with the completed metal electrode structure is subjected to low-temperature light injection. The temperature of the low-temperature light injection process is 150~300℃, the light intensity is 1~10 suns, and the processing time is 60~600s. The low-temperature light injection process is carried out in an atmosphere containing oxygen, ozone or trace amounts of water vapor to enhance the passivation and surface cleaning effects by synergistic effects of light, heat and oxidation atmosphere.

[0041] In the surface cleaning step: the surface cleaning method is at least one of ozone-based ultraviolet cleaning, plasma cleaning, and mild wet chemical cleaning.

[0042] A third objective of this invention is to provide a photovoltaic module comprising the solar cell described in any of the preceding claims. The photovoltaic module possesses all the technical features and effects of the aforementioned solar cell, which will not be elaborated further here. Attached Figure Description

[0043] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0044] Figure 1 This is a partial structural schematic diagram of a back-contact solar cell provided in an embodiment of the present invention; Figure 2 for Figure 1 Enlarged view of point A in the middle; Figure 3 This is a cross-sectional schematic diagram of a metal electrode structure provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of another metal electrode structure provided in an embodiment of the present invention; Figure 5 This is a partial schematic diagram of the back side of a back-contact solar cell provided in an embodiment of the present invention; Figure 6 for Figure 5 The diagram shows the structure of the trench in the implementation. Figure 7 A flowchart illustrating a method for preparing a photovoltaic cell according to an embodiment of the present invention; Figure 8 This is a schematic diagram of the photovoltaic cell manufacturing process provided in an embodiment of the present invention.

[0045] icon: 11-Trench; 111-Catching trench; 112-Collector trench; 12-Heavily doped layer; 13-Interface passivation layer; 14-Metal electrode structure; 141-Seed layer; 142-Electrode body layer; 143-Protective layer; 2-Silicon substrate. Detailed Implementation

[0046] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] It should be noted that in the description of this invention, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0048] It should be noted that in the description of this invention, the terms "connection" and "installation" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or a connection through an intermediate medium; they can refer to a mechanical connection or an electrical connection. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0049] Reference Figure 1 and Figure 2 The first aspect of this application provides a solar cell comprising: a silicon substrate 2; a trench 11 formed on the silicon substrate 2; a heavily doped layer 12 formed on the inner surface of the trench 11; an interface passivation layer 13 formed on the heavily doped layer 12; and a metal electrode structure 14 formed in the trench 11 and in contact with the interface passivation layer 13; wherein the doping concentration of the heavily doped layer 12 is greater than the doping concentration of the surrounding silicon substrate material.

[0050] The silicon substrate 2 has a light-facing surface for receiving light and an opposite back-light surface. A metal electrode structure 14 is disposed on at least one of the light-facing and back-light surfaces of the silicon substrate 2. The metal electrode structures 14 on the same surface are arranged according to a preset electrode pattern. All the metal electrode structures 14 are divided into a first metal electrode structure and a second metal electrode structure with different polarities. Figure 1 In the illustrated embodiment, a first metal electrode structure and a second metal electrode structure are alternately arranged along a first direction on the backlight surface; this embodiment is a back-contact solar cell. In other embodiments, a first metal electrode structure and a second metal electrode structure are alternately arranged along a first direction on both the light-facing and backlight surfaces; this embodiment is a bifacial solar cell, but it is not commonly found in the market. In still other embodiments, a first metal electrode structure is sequentially arranged along a first direction on the light-facing surface, and a second metal electrode structure is sequentially arranged along a first direction on the backlight surface; this embodiment is the most common bifacial solar cell on the market. All three types of solar cells described above are prior art, and their structures are not described in detail here.

[0051] The solar cells provided in this application can be any of the three types mentioned above. Among them, the metal electrode structure of the back-contact solar cell is entirely located on the back surface, and its electrode structure and fabrication process are more complex than those of bifacial cells. For back-contact solar cells, the mainstream process of forming the metal electrode structure using printed silver paste suffers from drawbacks such as high cost and limited printing precision, making it difficult to achieve finer electrode patterns with higher aspect ratios. To seek breakthroughs, the industry has explored an advanced process combining laser grooving with copper electroplating. While this process can achieve fine electrodes and reduce material costs, it still faces key bottlenecks: First, laser grooving causes severe thermal damage, resulting in rough groove walls with microcracks, leading to high recombination at the contact interface and affecting the adhesion of subsequent plating layers; second, copper electrodes are prone to oxidation and diffusion, resulting in poor stability and long-term reliability; third, currently, the contact resistance is generally reduced by increasing the doping concentration of the doped layer, but increasing the doping concentration leads to severe recombination problems.

[0052] The solar cell provided in this application employs a three-step synergistic process of "grooving—selective heavy doping—ultra-thin interface passivation," precisely constructing an electrode contact region with both ultra-low contact resistance and excellent interface passivation quality within a micrometer-level trench 11. This composite interface structure design ensures excellent ohmic contact between the metal and semiconductor while minimizing recombination losses in the contact area (i.e., the heavily doped layer 12) between the metal electrode structure 14 and the semiconductor. Simultaneously, the doping concentration in the non-electrode contact area of ​​the semiconductor is significantly lower than that in the heavily doped layer 12, providing a core guarantee for achieving a high open-circuit voltage and realizing the technical effects of high conductivity, low recombination, and low cost in solar cells. Furthermore, compared to conventional methods that form metal electrode structures through printing processes, the metal electrode structure 14 in this application is directly embedded within the trench 11, offering advantages such as a larger contact area, less electrode detachment, a smaller light-shielding area, and better surface flatness of the silicon substrate.

[0053] In some embodiments, the doping concentration of the heavily doped layer 12 is 1 × 10¹ 9atoms / cm³ ~1×10²¹ atoms / cm³; and / or, the doping concentration of the silicon substrate material surrounding the heavily doped layer 12 is 1×10¹. 5 atoms / cm³ ~1×10¹ 7 atoms / cm³; and / or, the ratio of the doping concentration of the heavily doped layer 12 to the doping concentration of the surrounding silicon substrate material is 100 : 1 to 10000 : 1. The doping concentration of the heavily doped layer 12 and the surrounding silicon substrate material can be selected from the above preferred range, and the doping concentration of the heavily doped layer 12 and the surrounding silicon substrate material should have a significant concentration difference.

[0054] In some embodiments, the cross-sectional shape of the groove 11 is at least one of trapezoidal, U-shaped, arc-shaped, rectangular, and triangular. The cross-sectional shape of the groove 11 can be selected from the above range.

[0055] Preferably, the cross-sectional shape of the groove 11 is trapezoidal. The trapezoidal groove design enables mechanical locking of the electrodes, improving the battery fill factor while giving the electrodes excellent mechanical adhesion and long-term reliability.

[0056] Reference Figure 3 When the cross-sectional shape of the trench 11 is trapezoidal, the opening area of ​​the trench 11 can increase from the bottom surface to the opening. With this cross-sectional configuration of the trench 11, the metal electrode structure 14, after being filled into the trench 11, forms a reliable interconnected self-locking structure with the trench 11. This increases the bonding strength between the metal electrode structure 14 and the silicon substrate 2, preventing the metal electrode structure 14 from detaching, improving the performance and reliability of the battery, and also increasing the contact area of ​​the solder ribbon of the metal electrode structure.

[0057] Reference Figure 4 When the cross-sectional shape of the groove 11 is trapezoidal, the opening area of ​​the groove 11 can also decrease from the bottom of the groove to the opening.

[0058] Reference Figure 5 and Figure 6In some embodiments, the trench 11 includes a busbar trench 111 and a collector trench 112. The busbar trench 111 extends along a second direction. At least one side of the width direction of the busbar trench 111 is arranged with a plurality of collector trenches 112 at intervals along the second direction. Each collector trench 112 extends along a first direction. The busbar trench 111 and the collector trench 112 are intersecting and connected. The first direction intersects (usually orthogonal) the second direction. The width of the busbar trench 111 is 80~300μm and its depth is 15~20μm. The width of each collector trench 112 is 20~40μm and its depth is 10~15μm. In the trench 11 provided in the above embodiment, the busbar trench 111 is used to fill the busbar electrode (commonly known as the main grid) for busing and connecting the external conductor, and the collector trench 112 is used to fill the collector electrode (commonly known as the fine grid) for collecting the current. The busbar electrode is generally wider and thicker than the collector electrode. Correspondingly, the busbar trench 111 generally needs to be wider and deeper than the collector trench 112.

[0059] In some other embodiments, the trench 11 may be an overall elongated strip structure. In still other embodiments, the trench 11 may include only the collector trench 112 and not the busbar trench 111; this structure of the trench 11 is applied in gridless solar cells.

[0060] In some embodiments, the material of the interface passivation layer 13 is at least one of silicon oxide, aluminum oxide, silicon oxynitride, silicon nitride, silicon carbide, and amorphous silicon; the thickness of the interface passivation layer 13 is 1~20 nm.

[0061] The material and thickness of the interface passivation layer 13 can be varied within the aforementioned preferred range. The main function of the interface passivation layer is to reduce surface recombination. The thickness of the interface passivation layer 13 should not be too thin, as this would lead to poor surface recombination reduction. Simultaneously, the thickness of the interface passivation layer should not be too thick, as this would affect carrier transport efficiency. Setting the thickness of the interface passivation layer within the range of 1~20 nm achieves a good reduction in surface recombination without affecting carrier transport efficiency. Preferably, the thickness of the interface passivation layer is 1~3 nm, a thickness range that ensures that the interface passivation layer can achieve carrier conduction.

[0062] Continue to refer to Figure 3 In some embodiments, the metal electrode structure 14 includes: a seed layer 141 covering the inner surface of the trench 11; an electrode body layer 142 disposed on the seed layer 141 and completely filling the trench 11; and a protective layer 143 covering the surface of the electrode body layer 142 exposed outside the trench 11.

[0063] The seed layer 141 covers at least the bottom surface of the trench 11 or the entire inner surface of the trench 11, and is a sintered conductive metal layer serving as the substrate for subsequent electroplating. The electrode body layer 142 is deposited on the seed layer 141 through an electroplating process and completely fills the trench 11, serving for carrier collection and current conduction. The protective layer 143 covers the surface of the electrode body layer 142 to prevent electrode oxidation and corrosion, improving the long-term reliability of the electrode. Furthermore, the protective layer 143 can interconnect with the silicon substrate 2 to form a mechanical locking structure of "in-trench filling + trench opening sealing," ensuring good ohmic contact while locking the electrode body layer 142 within the trench 11, thus preventing the electrode body layer 142 from peeling off.

[0064] In some embodiments, the seed layer 141 is made of at least one of silver, silver-aluminum alloy, and nickel, and its thickness is 0.5~3 μm; and / or, the electrode body layer 142 is an electroplated copper layer; and / or, the protective layer 143 is made of tin or a tin alloy, and its thickness is 0.5~3 μm. The materials and thicknesses of each layer of the metal electrode structure 14 can be selected from the preferred ranges described above.

[0065] In some embodiments, the metal electrode structure 14 protrudes a certain height relative to the surface of the trench 11. This structure of the metal electrode structure 14 protruding from the trench 11 has the following beneficial effects: it facilitates the interconnection between the electrode and the solder strip, avoiding the problem of poor contact between the electrode and the solder strip; it increases the cross-sectional area of ​​the electrode, thereby reducing the electrode resistance; and the protruding electrode can protect the heavily doped layer and the interface passivation layer inside the trench 11 from being damaged or destroyed by subsequent processes.

[0066] In other embodiments, the surface of the metal electrode structure 14 near the opening of the trench 11 is flush with the surface of the trench 11. This structure, where the surface of the metal electrode structure 14 is flush with the surface of the trench 11, has the following advantages: high flatness of the silicon substrate surface and small light-shielding area, reducing the risk of the electrode being bumped or damaged by the external environment. However, this structure is not conducive to the interconnection of the electrode and the solder ribbon, and is more suitable for applications involving metal wiring connections.

[0067] A second aspect of the present invention provides a method for preparing a photovoltaic cell, referring to... Figure 7 and Figure 8 The method includes the following steps: S1 provides a silicon substrate 2, performs front passivation and back passivation treatment on the silicon substrate 2, and deposits an insulating film on the light-facing side and the back-facing side of the silicon substrate 2 respectively.

[0068] S2, Laser grooving: A high-precision laser processing system is used to perform laser scanning on a preset position on the silicon substrate 2 according to a preset pattern to form fine grooves 11.

[0069] For back-contact solar cells, trenches 11 only need to be fabricated on the back surface of the silicon substrate 2. In a back-contact solar cell, P-type doped regions and N-type doped regions are formed alternately along a first direction on the back surface of the silicon substrate 2, and a corresponding trench 11 is fabricated at each P-type doped region and each N-type doped region.

[0070] For bifacial solar cells, trenches 11 need to be processed on the light-facing and back-facing surfaces of the silicon substrate 2, and the processing order of the trenches 11 on the light-facing surface and the back-facing surface is not important.

[0071] Optionally, before performing front and back passivation on the silicon substrate 2, a low-concentration doped layer can be formed in each P-type doped region and each N-type doped region by laser doping or high-temperature diffusion process. The doping concentration of the low-concentration doped layer needs to be significantly lower than that of the subsequently formed heavily doped layer 12.

[0072] Optionally, for a back-contact solar cell, the trench 11 includes a current-collecting trench 111 and a current-collecting trench 112. The current-collecting trench 111 extends along a second direction, and at least one side of the width direction of the current-collecting trench 111 is arranged with a plurality of current-collecting trenches 112 at intervals along the second direction. Each current-collecting trench 112 extends along a first direction, and the current-collecting trench 111 and the current-collecting trench 112 are intersecting and connected. The cross-sectional area of ​​the current-collecting trench 111 is larger than the cross-sectional area of ​​the current-collecting trench 112. The width of the current-collecting trench 111 is 80~300μm and its depth is 15~20μm. The width of each current-collecting trench 112 is 20~40μm and its depth is 10~15μm.

[0073] Optionally, in the laser grooving step: a UV picosecond laser (wavelength 355nm) or an infrared picosecond laser (wavelength 1064nm) is used for laser scanning. The laser scanning parameters are: single pulse energy of 10~50μJ, repetition frequency of 50~500kHz, and scanning speed of 0.5~5m / s. During the laser scanning process, high-purity nitrogen or argon is used for side blowing to remove the molten material in a timely manner, resulting in a smooth inner surface groove 11. Compared with an infrared picosecond laser, the advantage of using a UV picosecond laser for laser scanning is less damage to the silicon substrate 2, while the disadvantages are slower processing speed and higher cost. If fine patterning of the groove 11 is required, a UV picosecond laser is preferred for laser scanning.

[0074] S3, Cleaning trench 11: Soak or spray trench 11 with chemical cleaning solution at room temperature, rinse with ultrapure water and dry with nitrogen after treatment.

[0075] In the cleaning step of trench 11, trench 11 is immersed or sprayed with a 1%~5% (w / w) dilute hydrofluoric acid HF solution and / or buffered oxide etchant BOE at room temperature for 30~180s. This method thoroughly removes the amorphous silicon layer, oxide layer, and residual contaminants generated by the laser thermal effect, laying the foundation for achieving both ultra-low contact resistance and ultra-low interface recombination simultaneously within the trench.

[0076] S4, Forming a heavily doped layer 12: A heavily doped layer 12 is formed on the inner surface region of the trench 11 using a laser doping process. This step specifically includes: coating a boron- or phosphorus-containing liquid composition into the trench 11; after pre-drying, using a laser beam to precisely scan the trench 11, causing localized melting of the silicon substrate material within the trench 11 and incorporation of boron or phosphorus atoms, forming a P-type or N-type heavily doped layer 12. During solar cell fabrication, the doping order of the P-type and N-type doped regions is not critical; the P-type doped region can be formed first, followed by the N-type doped region, or vice versa. After doping, the solar cell is cleaned to remove any remaining dopant.

[0077] In the step of forming the heavily doped layer 12: the pre-drying temperature after coating with the boron- or phosphorus-containing liquid composition is 100~200°C and the time is 60~300s; the laser beam is a continuous wave laser or a long pulse laser with a pulse width greater than 1μs, and the scanning speed is 1~10m / s; for the P-type heavily doped layer 12, the laser scanning power is 10~50W; for the N-type heavily doped layer 12, the laser scanning power is 8~40W.

[0078] S5, Annealing treatment: The annealing treatment is carried out using a rapid thermal annealing process in a nitrogen or argon atmosphere. The annealing temperature is 800~1000℃ and the annealing time is 10~60s.

[0079] Annealing the structure can repair defects and surface damage caused by the etching process, and can also effectively activate impurities, providing a basic guarantee for achieving ultra-low contact resistance and ultra-low interface composite in the future.

[0080] S6, forming an interface passivation layer 13: an interface passivation layer 13 is formed on the inner surface of the trench 11 by a deposition process, wherein the deposition process is one or a combination of atomic layer deposition (ALD), plasma enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD).

[0081] The steps S1 to S6 described above aim to repair the lattice damage caused by laser grooving and construct a high-performance local contact area, laying the foundation for the subsequent formation of the metal electrode structure 14.

[0082] S7, forming a metal electrode structure 14 filling the trench 11, including: S71, Printing and Sintering Seed Layer 141: Conductive paste is filled into the trench 11, pre-dried, and then sintered at a low temperature to form a seed layer 141 covering the inner surface of the trench 11; wherein: the pre-drying temperature is 100~200℃, and the time is 60~300s; the peak temperature of the low-temperature sintering is 250~450℃, and the holding time is 30~300s; the thickness of the seed layer 141 after drying is 1~5μm; the step of filling the conductive paste into the trench 11 can be achieved by printing or inkjet printing process; S72, Deposited electrode body layer 142: Using seed layer 141 as cathode, copper material is deposited on seed layer 141 by electroplating until the copper material fills trench 11 and forms electrode body layer 142 protruding from the surface of trench 11; wherein: the electroplating process is pulse electroplating or DC electroplating process, the plating solution contains copper ions, acid, conductive salt, chloride ions and organic additives, the electroplating process is carried out at a temperature of 20~60°C, and the cathode current density is 1~10A / dm²; S73, Deposited protective layer 143, is formed on the surface of the electrode body layer 142 exposed outside the trench 11 by a deposition process. The deposition process is one of electroplating deposition, electroless plating deposition, or hot-dip plating deposition. The thickness of the protective layer 143 is 0.5~3μm. The protective layer 143 is tin or a tin alloy, wherein the tin alloy is one or a combination of several of tin-silver alloy, tin-bismuth alloy, and tin-copper alloy.

[0083] S8, Light Injection Treatment and Surface Cleaning: The solar cells with completed electrode fabrication are subjected to low-temperature light injection treatment. The temperature of the low-temperature light injection treatment is 150~300℃, the light intensity is 1~10 suns, and the treatment time is 60~600s. The low-temperature light treatment is carried out in an atmosphere containing oxygen, ozone, or trace amounts of water vapor to enhance the passivation and surface cleaning effects by synergistic effects of light, heat, and oxidizing atmosphere. The surface cleaning method is at least one of ozone-based ultraviolet light cleaning, plasma cleaning, and mild wet chemical cleaning.

[0084] Compared to existing methods that form metal electrode structures through printing or electroplating processes, this method has the following advantages: (1) A heavily doped layer 12 is formed on the inner surface region of the trench 11 to achieve ultra-low contact resistance; and an interface passivation layer 13 is added between the metal electrode structure and the inner surface of the trench 11. The interface passivation layer 13 can reduce the recombination rate of the metal-semiconductor interface on the one hand, and enhance the adhesion of the metal electrode structure on the other hand, thus avoiding the risk of the metal electrode structure falling off; the doping concentration of the heavily doped layer 12 is significantly higher than that of the surrounding silicon substrate material to reduce surface recombination.

[0085] (2) The metal electrode structure 14 formed by this method is directly embedded in the trench 11, which has the advantages of larger contact area, less electrode detachment, smaller battery light-shielding area and better surface flatness of silicon substrate.

[0086] (3) A composite process of “printed nano-seed layer + electroplated copper + deposited protective layer” was used to prepare the metal electrode structure, which achieved high-precision forming and ultra-low volume resistance of the metal electrode structure. Among them, the electrode body layer 142 can perfectly fill the groove and reliably interconnect, while the protective layer 143 ensures the long-term corrosion resistance of the electrode body layer 142; the protective layer 143 can also interconnect with the silicon substrate 2 to form a mechanical locking structure of “groove filling + groove sealing”, which ensures good ohmic contact while locking the electrode body layer 142 in the groove 11, thereby preventing the electrode body layer 142 from peeling off.

[0087] (4) By combining chemical cleaning, heavy doping, annealing and ultrathin interface passivation, the lattice damage caused by laser grooving is repaired and a high-performance local contact area is constructed, laying a good foundation for the formation of the subsequent metal electrode structure 14, and realizing the technical effects of high conductivity, low recombination and low cost of solar cells.

[0088] (5) The use of efficient laser doping technology to replace part of the high-temperature diffusion doping technology can significantly improve the battery conversion efficiency while greatly reducing the manufacturing cost of the electrode, thus having outstanding industrial application prospects and market competitiveness.

[0089] A third aspect of the present invention provides a photovoltaic module comprising the solar cell provided in any of the above embodiments. This photovoltaic module possesses at least all the technical features and effects of the aforementioned solar cell, which will not be repeated here.

[0090] Performance testing The following types of solar cells were selected as samples for performance testing: Test Sample 1: A solar cell formed using the above method, wherein the metal electrode structure 14 consists of a seed layer 141, an electroplated copper electrode body layer 142, and a protective layer 143, and the cross-sectional shape of the trench 11 is as follows. Figure 3 The trapezoid shown.

[0091] Test Sample 2: The only difference between it and Sample 1 is the cross-sectional shape of its groove 11. Figure 4 The trapezoid shown.

[0092] Test Sample 3: The only difference between it and Sample 1 is that the cross-sectional shape of its groove 11 is rectangular.

[0093] Test sample four: The only difference between it and sample one is that it does not have a protective layer 143.

[0094] Test sample five: The only difference from sample one is that its metal electrode structure 14 is fabricated by screen printing silver paste process.

[0095] Test sample six: The only difference from sample one is that it has no interface passivation layer 13.

[0096] Comparison sample one: A conventional non-grooved solar cell with its metal electrode structure fabricated by screen printing silver paste process, and it has no heavily doped layer 12 and interface passivation layer 13.

[0097] Comparison sample two: A conventional grooved solar cell with its metal electrode structure fabricated by electroplating copper process, and it has no heavily doped layer 12 (i.e., the doping concentration in the inner surface area of the groove is equal to that of the surrounding silicon substrate material, with no obvious concentration gradient change) and interface passivation layer 13.

[0098] The test methods are as follows: Electrical performance test: IV test is adopted (test conditions: AM1.5G spectrum, light intensity of 1000 W / m², temperature of 25°C) to detect parameters such as the photoelectric conversion efficiency, open-circuit voltage, series resistance, and fill factor of the battery.

[0099] Test for the bonding force between the electrode and the silicon substrate: First, fix the silicon substrate 2. Then, use 3M tape to stick and cover a certain metal electrode structure 14. After that, quickly tear the tape at a 90° angle until the tape is completely separated from the metal electrode structure 14. If the metal electrode structure 14 does not fall off and there is no metal residue on the tape, it is qualified. Using the above method, conduct the bonding force test on at least 20 metal electrode structures 14 in each sample respectively, and record the qualification rate of the electrode bonding force for each sample.

[0100] Test for contact resistivity: Cut the solar cell into small strips along the extension direction of the bus electrode (i.e., the main grid), and use the four-probe method to measure the sheet resistance of the metal electrode structures 14 in the P region and N region respectively, and calculate the contact resistivity (mΩ·cm²); measure at least 10 small strips for each sample and take the average value.

[0101] The test results are shown in Table 1.

[0102] Table 1

[0103] It can be seen from the test results in Table 1 that: (1) The overall performance of the test sample 1 (the optimal embodiment of the present invention) is the best, achieving a photoelectric conversion efficiency of 26.25%, an electrode bonding force qualification rate of 100%, and a low contact resistivity of 0.55 mΩ·cm². All indicators are significantly better than other samples. The comparison of groove shapes shows that the trapezoidal structure with a narrow top and a wide bottom has a better contact resistivity (0.55) and electrode bonding force qualification rate (100%) than the trapezoidal structure with a wide top and a narrow bottom and the rectangle due to the mechanical locking effect of the "dovetail groove".

[0104] (2) The protective layer 143 has a significant effect. The pass rate of electrode bonding force of test sample 1 with protective layer 143 is 5% higher than that of test sample 4 without protective layer 143.

[0105] (3) Regarding the electrode formation method, the efficiency of the electroplated copper electrode (test sample 1) is increased by 0.37 percentage points and the contact resistivity is reduced by 42.7% compared with the silver electrode (test sample 5).

[0106] (4) The interface passivation layer 13 improves efficiency by 0.5 percentage points and reduces contact resistivity by 40.2%.

[0107] (5) Compared with the first comparative sample (conventional screen printing), the efficiency of the present invention is increased by 0.61 percentage points and the contact resistivity is reduced by 61.8%; compared with the second comparative sample (simple grooving + copper electroplating), the efficiency of the present invention is increased by 1.05 percentage points and the contact resistivity is reduced by 56.0%.

[0108] In summary, this embodiment achieves a high-efficiency and high-reliability back-contact solar cell through the synergistic optimization of the trapezoidal trench 11 (narrower at the top and wider at the bottom), the heavily doped layer 12, the interface passivation layer 13, the electroplated copper electrode, and the protective layer.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solar cell, characterized in that, include: Silicon substrate (2); Trench (11) is formed on the silicon substrate (2); A heavily doped layer (12) is formed on the inner surface of the trench (11); An interface passivation layer (13) is formed on the heavily doped layer (12); A metal electrode structure (14) is formed in the trench (11) and is in contact with the interface passivation layer (13); The doping concentration of the heavily doped layer (12) is greater than that of the silicon substrate material surrounding it.

2. The solar cell according to claim 1, characterized in that, The doping concentration of the heavily doped layer (12) is 1 x 1018 atoms / cm3 ~ 1 x 1021 atoms / cm3. 9 atoms / cm3 ~ 1 x 1021 atoms / cm3. and / or the doping concentration of the silicon base material around the heavily doped layer (12) is 1 x 1015 5 atoms / cm³ ~ 1 x 1016 7 atoms / cm³; And / or, the ratio of the doping concentration of the heavily doped layer (12) to the doping concentration of the surrounding silicon substrate material is 100:1 to 10000:1; And / or, the material of the interface passivation layer (13) is at least one of silicon oxide, aluminum oxide, silicon oxynitride, silicon nitride, silicon carbide, and amorphous silicon; And / or, the thickness of the interface passivation layer (13) is 1~20 nm; And / or, the metal electrode structure (14) protrudes a certain height relative to the surface where the groove (11) is located, or, the surface of the metal electrode structure (14) near the opening of the groove (11) is flush with the surface where the groove (11) is located.

3. The solar cell according to claim 1, characterized in that, The cross-sectional shape of the groove (11) is at least one of trapezoidal, U-shaped, arc-shaped, rectangular, and triangular; preferably, the cross-sectional shape of the groove (11) is trapezoidal. And / or, the opening area of ​​the groove (11) increases from the bottom surface of the groove to the opening of the groove; And / or, the trench (11) includes a merging trench (111) and a collecting trench (112), the merging trench (111) extends along a second direction, and at least one side of the merging trench (111) in the width direction is arranged with a plurality of collecting trenches (112) at intervals along the second direction, each collecting trench (112) extends along a first direction, the merging trench (111) and the collecting trench (112) are intersecting and connected, and the first direction intersects the second direction; the width of the merging trench (111) is 80~300μm and its depth is 15~20μm; the width of each collecting trench (112) is 20~40μm and its depth is 10~15μm.

4. The solar cell according to claim 1, characterized in that, The metal electrode structure (14) includes: A seed layer (141) covers the inner surface of the groove (11); The electrode body layer (142) is disposed on the seed layer (141) and completely fills the trench (11). A protective layer (143) covers the surface of the electrode body layer (142) exposed outside the trench (11).

5. The solar cell according to claim 4, characterized in that, The seed layer (141) is made of at least one of silver, silver-aluminum alloy, and nickel; And / or, the thickness of the seed layer (141) is 0.5~3μm; And / or, the electrode body layer (142) is an electroplated copper layer; And / or, the protective layer (143) is made of tin or a tin alloy; And / or, the thickness of the protective layer (143) is 0.5~3μm.

6. A method for preparing a photovoltaic cell, characterized in that, Includes the following steps: Provide silicon substrate (2); Laser grooving: Laser scanning is performed at a preset position on the silicon substrate (2) according to a preset pattern to form a groove (11). Forming a heavily doped layer (12): A heavily doped layer (12) is formed on the inner surface region of the trench (11) by laser doping process, wherein the doping concentration of the heavily doped layer (12) is greater than the doping concentration of the surrounding silicon substrate material; Forming an interface passivation layer (13): An interface passivation layer (13) is formed on the inner surface of the trench (11) by a deposition process. A metal electrode structure (14) is formed that fills the trench (11).

7. The method for preparing a photovoltaic cell according to claim 6, characterized in that, The step of forming the metal electrode structure (14) filling the trench (11) includes: Printing and sintering seed layer (141): The conductive paste is filled into the trench (11), pre-dried and then sintered at low temperature to form a seed layer (141) covering the inner surface of the trench (11). Electrode body layer (142): Using the seed layer (141) as the cathode, copper material is deposited on the seed layer (141) by electroplating until the copper material fills the trench (11) and forms an electrode body layer (142) protruding from the surface of the trench (11). A protective layer (143) is deposited, which is formed on the surface of the electrode body layer (142) exposed outside the trench (11) by a deposition process.

8. The method for preparing a photovoltaic cell according to claim 7, characterized in that, In the steps of printing and sintering the seed layer (141): the pre-drying temperature is 100~200℃ and the time is 60~300s; the peak temperature of low-temperature sintering is 250~450℃ and the holding time is 30~300s; the thickness of the seed layer (141) after drying is 1~5μm; And / or, in the step of depositing the electrode body layer (142): the electroplating process is pulse electroplating or DC electroplating; the plating solution used contains copper ions, acid, conductive salt, chloride ions and organic additives; the electroplating process is carried out at a temperature of 20~60°C; the cathode current density is 1~10A / dm². And / or, in the step of depositing the protective layer (143): the type of deposition process is one of electroplating deposition, electroless plating deposition, or hot-dip plating deposition; the thickness of the protective layer (143) is 0.5~3μm.

9. The method for preparing a photovoltaic cell according to claim 6, characterized in that, In the laser grooving step: an ultraviolet picosecond laser or an infrared picosecond laser is used for laser scanning. The laser scanning parameters are a single pulse energy of 10~50μJ, a repetition frequency of 50~500kHz, and a scanning speed of 0.5~5m / s. Gas side blowing is used to remove the molten material during the laser scanning process. And / or, after the laser grooving step, the method for preparing the photovoltaic cell further includes: cleaning the trench (11): soaking or spraying the trench (11) with a chemical cleaning solution at room temperature, rinsing with ultrapure water and drying with nitrogen after the treatment is completed; And / or, the step of forming the heavily doped layer (12) includes: coating a liquid composition containing boron or phosphorus into the trench (11), pre-drying it, and then using a laser beam to precisely scan the trench (11) to locally melt the silicon substrate material in the trench (11) and incorporate boron or phosphorus atoms to form a heavily doped layer (12) of P-type or N-type doping. And / or, after the step of forming the heavily doped layer (12), the method for preparing the photovoltaic cell further includes: annealing treatment; And / or, after the step of forming the metal electrode structure (14) filling the trench (11), the method of preparing the photovoltaic cell further includes: light injection treatment and surface cleaning.

10. A photovoltaic module, characterized in that, Including the solar cell as described in any one of claims 1 to 5.

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